A sleeve-shaped printing plate to be used for various kinds of printing, as in, for example, Patent Document 1, is fitted through a printing plate cylinder, and thereby fixed so as to come into close contact with the outer circumferential surface of the printing plate cylinder. A conventional printing plate cylinder is formed substantially in a cylindrical shape which has a hollow air chamber, and is constructed to form an air supply hole which penetrates into the air chamber from an axial end surface thereof, and an air outlet hole which penetrates into the air chamber from an outer circumferential surface thereof.
In this printing plate cylinder, when air is introduced into the air chamber from the air supply hole to raise the pressure of the air chamber in a state where the printing plate is fixed to the outer circumferential surface of the printing plate cylinder so as to block the air outlet, high-pressure air is blown off through the air outlet with this pressure rise. Accordingly, when the printing plate is attached to and detached from the printing plate cylinder, since the printing plate can be inflated radially outward by the high-pressure air which is blown off through the air outlet, the printing plate can be easily attached and detached.
Additionally, the following one is conventionally known as a common problem related to the printing quality in a printing apparatus under operation. That is, in the cylindrical printing plate cylinder having the printing plate, to which a printing design (image portion) is given, on the outer circumferential surface thereof, at the time of printing, the surface temperature of the printing plate is gradually raised due to frictional heat with a blanket in contact with the printing plate or the conduction of heat from a driving shaft side which supports a rotating shaft portion, and accordingly ink temperature rises, and ink viscosity decreases. As a result, ink spread, color tones or the like vary, and printing quality is reduced. Additionally, in a waterless planographic plate, it is known that such a temperature rise of the printing plate cylinder promotes deterioration of the printing plate.
In order to prevent such a phenomenon, for example, in a printing apparatus disclosed in Patent Document 2, cold air is forcibly applied to a shaft portion of a rotating printing plate cylinder, and the temperature of the printing plate cylinder and the printing plate is lowered for cooling.
Meanwhile, in recent years, there is known a CTS (Computer To plate on Sleeve) technique of using a cylindrical sleeve member on the outer circumferential surface of which a printing plate is installed, directly laser-machining the printing plate to form an image portion, and then allowing attachment and detachment of each sleeve member to/from the printing plate cylinder. According to this CTS technique, positioning of the printing plate can be easily performed with high accuracy, and the operation process for forming an image portion on the printing plate and replacement (attachment and detachment) of the printing plate can be simply and easily performed. Thus, productivity is remarkably increased.
Generally, a two-piece can to be used as a container, such as for soft drinks, is composed of a can lid, and a can barrel which is a cylindrical body. The can barrel is subjected to DI (deep-drawing, ironing) work and cleaning, and then printing is performed on the outer surface of the can barrel. When a cylindrical object, such as the can barrel, is printed, for example, the offset printing apparatus using offset printing as shown in Patent Document 1 is used.
Such an offset printing apparatus includes a plurality of printing plate cylinders which forms a substantially columnar shape or a substantially cylindrical shape, and has a printing plate composed of a relief printing plate or the like on the cylindrical surface, and a blanket cylinder which rotates in synchronization with these printing plate cylinders, and has a blanket made of rubber disposed on the outer circumferential surface, and the printing plates of the printing plate cylinders and the blanket of the blanket cylinder come into contact with each other. Ink is applied to the printing plate of each printing plate cylinder, this ink is transferred to the blanket, and this blanket comes into contact with the outer circumferential surface of the can barrel so that printing is performed on the outer circumferential surface of the can barrel.
In such a printing plate cylinder, since it is necessary to arrange the printing plate with high accuracy on the cylindrical surface, the stability of the external diameter is required. Additionally, since the printing plate cylinder is attached to and detached from a rotary shaft of the printing apparatus, the accuracy of the shape of the portion in which the rotary shaft is fitted is required. For this reason, generally, the conventional printing plate cylinder has relatively high rigidity, and is constituted of carbon steel having excellent workability.
[Patent Document 1] Japanese Patent Unexamined Publication No. 2007-44987
[Patent Document 2] Japanese Patent Unexamined Publication No. 2002-347214